There is a consensus that overt diabetes mellitus (DM), whether or not accompanied by symptoms or signs of metabolic decompensation, is associated with a significant risk of adverse pregnancy outcome. On the other hand, the risk of adverse outcome associated with degrees of glucose intolerance less severe than overt DM is controversial. The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study is a basic epidemiologic investigation aiming to clarify unanswered questions on the association of various levels of glucose intolerance during the third trimester of pregnancy and risk of adverse outcomes. Its General Aim, by means of an international cooperative study involving 16 field centers and approximately 25,000 pregnant women, is to achieve a major advance in knowledge on levels of glucose during pregnancy that place the mother, fetus, and neonate at increased risk. The primary hypothesis is that hyperglycemia, less severe than overt DM, is associated with increased risk of adverse maternal, fetal, and neonatal outcome that is independently related to the degree of metabolic disturbance. Specific Aims of HAPO are: 1. To examine glucose tolerance in a large, heterogeneous, multinational, multicultural, ethnically diverse cohort of women in the third trimester of gestation with medical caregivers "blinded" to status of glucose tolerance (except in those instances where fasting and/or two hour OGTT plasma glucose concentration exceeds a predefined cutoff value); and 2. To provide data that can be used to derive internationally acceptable criteria for the diagnosis and classification of gestational diabetes mellitus (GDM) based on the identification of pregnancies at risk for specific adverse outcomes. The study is to be accomplished with high quality standardized data collection on the women during the third trimester of gestation (including the OGTT) and at time of delivery for assessment of adverse outcomes, including fetal hyperinsulinism, fetal obesity (macrosomia), operative delivery (caesarian section), and neonatal morbidity (hypoglycemia). HAPO is to include field centers and regional centers where the participants will be studied, a Clinical Coordinating Center and Data Coordinating Center, both located at the Northwestern University Medical School in Chicago, as well as a Central Laboratory located in Belfast, Northern Ireland. This application requests support for the Clinical Coordinating Center, the field and regional centers and Central Laboratory. Cost effectiveness for the HAPO study is enhanced through cost sharing by colleagues in non-U.S. centers.